Nairobi - The Kenyan police on Thursday warned of a major crackdown in the northern town of Mandera near the border with Somalia, where Al-Shabaab suspects killed a police officer and injured five others in the past two days.

Inspector General of Police David Kimaiyo said so far no suspect has been arrested in connection to the incident which saw the officers who were on normal patrol killed by an explosion which was planted by roadside.

"Our initial investigation into this matter indicate that this might have been a device which had been in place for some time, because of the fact that of late, we have managed to bring hostile activities under check," Kimaiyo said in a statement read by his spokesman Mosoud Mwinyi.

The six officers - four police officers and two administration police, were patrolling on foot but a device exploded when they went under a tree to rest, killing a police officer and injuring five others.

The police have not established whether the device was an Improvised Explosive Device (IED) or Rocket Propelled Grenade (RPG) but noted that the officers had multiple injuries and have been rushed to the hospital.

"We are nonetheless, still investigating the incident. However, I wish to give notice to the attackers that their days are numbered and soon they will face the full force of the law," Kimaiyo said.

The police boss encouraged all security officers to be on the lookout and deal with the criminals decisively and in accordance with the law.

He said the injured officers have been flown to Nairobi for specialized treatment, adding that the police are monitoring their progress.

"We condole with the family, friends and relatives of the gallant officer who lost his life while serving our great nation and pray that God gives them support and comfort during this trying moment," Kimaiyo said.

An Improvised explosive device is common in the northern Kenya after two people were also killed late last year when the device they were planting on a roadside targeting security officer accidentally went off in Dadaab killing them instantly.

Kenyan security personnel patrolling the border with Somalis have suffered a series of explosion attacks since Kenya sent its troops to fight Al-Shabaab inside Somalia in October 2011.

Garissa and Mandera regions have been the worst hit the attacks that have been targeting police officers and civilians.